1. Field of the Invention
The field of art to which this invention pertains is a color television camera and in particular to a color modulating system for such cameras.
2. Description of the Prior Art
Color cameras have been developed in the prior art using CCD's where at least two of three primary colors, R, G and B, are obtained in a line sequential manner. In such systems, signals from adjacent two lines must be mixed together in order to develop a simultaneous color composite signal for each scan line. The simultaneous color composite signal is a color signal modulated at a subcarrier frequency and is represented by a chroma signal of the NTSC color composite type signal.
In such a prior art system, R and B, for example, are obtained in a line sequential manner. Upon generating a simultaneous color composite signal for a certain line, such as the (2n + 1)nth line, where n=0, 1, 2, . . . , R and G on the (2n + 1)th line and B on the (2n)th line are mixed. In this case, color difference signals E.sub.B-Y and E.sub.R-Y on (2n + 1)th line are expressed as follows: EQU E.sub.R-Y = R(2n + 1) - Y(C) = 0.7R(2n + 1) - 0.59G(2n + 1) - 0.11B(2n) EQU E.sub.B-Y = B(2n) - Y(C) = 0.89B(2n) - 0.59G(2n + 1) - 0.30R(2n + 1)
where Y(C) is a luminance signal and is expressed as follows: EQU Y(C) = 0.30R(2n + 1) + 0.59G(2n + 1) + 0.11B(2n).
In this case, respective color signals are EQU E.sub.R = R(2n + 1) EQU E.sub.G = G(2n + 1) + 1.695[Y(C) - Y(N)] EQU = g(2n + 1) + 1.695 .multidot. 0.11[B(2n) - B(2n + 1)] EQU E.sub.B = B(2n)
wherein Y(N) is a standard luminance signal of the NTSC color system type on the (2n + 1)th scan line and is expressed as follows: EQU Y(N) = 0.30R(2n + 1) + 0.59G(2n + 1) + 0.11B(2n + 1).
Assuming that B(2n) = B(2n + 1), E.sub.G and E.sub.B are expressed as follows: EQU E.sub.G = G(2n + 1) EQU E.sub.B = B(2n + 1).
If the vertical correlation of adjacent lines is sufficiently strong, color dot signals at the edge of a black and white object are not visible. On the contrary, such dot-like patterns are undesirably visible when there is little or no vertical correlation between signals from adjacent lines. This is an extremely unfavorable characteristic.